Skip to content U.S. Department of Transportation/Federal Highway AdministrationU.S. Department of Transportation/Federal Highway Administration
Office of Planning, Environment, & Realty (HEP)

Assessing the Effects of Freight Movement on Air Quality at the National and Regional Level


The U.S. economy is dependent on an efficient and reliable freight transportation system. Our highways, ports, waterways, railways, airports, and intermodal facilities make up a complex system that shippers rely on to move products to markets. The performance of that system has direct implications for the productivity of the U.S. and regional economies, the costs of goods and services, and the global competitiveness of our industries. Yet, there is significant and growing concern on the part of both the private and public sectors about the future performance of our freight transportation system. Consider the following trends:

Prompted by these trends, federal, state, and local agencies are undertaking a variety of initiatives to ensure that the performance of the nation's freight system does not significantly deteriorate. For example, government agencies are exploring a variety of opportunities to fund freight system improvements, including expanded use of discretionary surface transportation funds, new public-private partnerships, and development of new sources of revenue for freight projects. Metropolitan Planning Organizations (MPOs) and state Departments of Transportation (DOTs) are working to mainstream freight into the transportation planning and programming process. Integration efforts include greater involvement of freight stakeholders throughout the planning process, application of project selection criteria that explicitly account for freight benefits, and use of performance measures to track progress toward freight mobility goals. At the federal level, the Federal Highway Administration (FHWA) and other agencies are supporting professional development related to freight transportation through training and information sharing; federal agencies are also developing a number of analytical tools to assist in freight transportation planning and impact assessment.

As freight becomes more integrated into the transportation planning and programming process, there is greater need to consider the air quality impacts of freight at all stages of planning and project development. Over the last two decades, freight has become a more significant source of air pollution. One reason for this is the robust growth in freight activity described above. The other factor is the relatively less stringent regulation on emissions from the freight sector compared to passenger vehicles. Although the U.S. Environmental Protection Agency (EPA) has recently issued strict new nitrogen oxides (NOx) and particulate matter (PM) emission standards for heavy-duty trucks, these standards do not begin to take effect until 2007 and then will take some time to ripple throughout the nation's truck fleet. The major non-road freight modes (locomotives and marine vessels) were virtually unregulated until the late 1990s, and today remain much less regulated than on-road sources. Fortunately, many locomotives, ships, and aircraft have become more fuel efficient over time, which tends to reduce pollutant emissions.

The implications of these trends can be summarized as follows:

At the same time that freight transportation's contribution to air pollution is growing, there is a heightened concern about the health and environmental effects of diesel engine emissions. Most freight trucks, locomotives, and ships are powered by diesel engines, which are a major source of emissions of NOx and PM. Freight transportation is also a large and growing source of greenhouse gas (GHG) emissions that contribute to global climate change, particularly carbon dioxide (CO2) emissions. These concerns, and the implementation of the 8-hour ozone and fine particulate (PM-2.5) standards, will require many regions across the country to find new ways to control NOx and PM emissions from freight transportation sources.

This study is intended to help fill a void in the current understanding of the air quality impacts of freight transportation. A large body of research has looked at multimodal freight flows from a transportation and economic perspective, and many other studies have examined the air quality impacts of freight transportation for a single mode. A smaller number of studies have compared fuel efficiency or emissions across two or more freight modes in an intercity context, but very few studies have examined freight transportation and emissions within urban areas. Furthermore, emission inventories prepared for air quality planning purposes, many of which were reviewed for this study, typically do not distinguish between freight and non-freight activity and may not allow comparison across modes or cities.

This report discusses freight transportation activity and emissions at the national level and in six metropolitan areas (Baltimore, Chicago, Dallas-Fort Worth, Detroit, Houston, and Los Angeles). The report draws on a variety of existing studies and data sources and develops new emissions estimates to fill data gaps. The study findings were documented in six detailed technical memoranda prepared by ICF Consulting for FHWA over the course of 2004. This report presents selected highlights from those memoranda.

The remainder of this report is organized into four sections:

Several appendices (Appendix A, Appendix B, Appendix C) provide supporting technical information.

Updated: 8/12/2014
HEP Home Planning Environment Real Estate
Federal Highway Administration | 1200 New Jersey Avenue, SE | Washington, DC 20590 | 202-366-4000